Stone
Building Material Civil Engineering
A good building stone has the following properties:
- Percentage of wear in the attrition test should not be more than 3
- Specific gravity should be at least 2.7
- Coefficient of hardness should be greater than 17
- Percentage of water absorption by weight of stone should be less than 5
- Toughness index should not be less than 13
- Crushing strength should be greater than 100 N/mm2
Test on stone
Building stones are available in large quantities in various parts of the country and to choose and utilize them for their satisfactory performance, it is necessary to test the stone for its strength properties, durability and quality.
Durability Test
The durability (soundness) test is performed to find out the capacity of stone to resist disintegration and decomposition.
Some of the tests to check the durability of stone are as follows.
1. Smith's Test
Break off the freshly quarried stone chippings to about the size of a rupee coin and put them in a glass of clean water, one-third full.
If the water becomes slightly cloudy, the stone is good and durable.
If the water becomes dirty, it indicates that the stone contains too much of earthy and mineral matter.
2. Brard's Test - for frost resistance
Few small pieces of freshly quarried stone are immersed in a boiling solution of sulphate of soda (Glauber’s salt) and are weighed.
These are then removed and kept suspended for few days and weighed again.
The loss in weight indicates the probable effect of frost.
3. Acid Test - to check weather resistance
It confirms the power of stones to withstand atmospheric conditions.
100 g of stone chips are kept in a 5 percent solution of H2SO4 or HCI for 3 days.
Then the chips are taken out and dried.
The sharp and firm corners and edges are indications of sound stone.
4. Crystallization Test (IS 1126)
Three test pieces of 50 mm diameter and 50 mm height are dried for 24 hours and are weighed (W1).
The specimens are suspended in 14 percent sodium sulphate solution (density 1.055 kg/m3) for 16 to 18 hours at room temperature (20° to 30°C).
The specimens are then taken out of the solution and kept in air for 4 hours.
They are then oven-dried at a temperature of 105° ± 5°C for 24 hours and then cooled at room temperature.
This process is repeated for 30 cycles.
The specimens are weighed (W2) and the difference in weight is found.
This test is repeated thirty times and the loss in weight after every five cycles is obtained.
The change in weight indicates the degree of decay of stone.
Durability should be expressed in percentage as the change in the weight. The average of three test results should be reported as durability value.
Change in weight = (W1 - W2) / W1
where W1 is the original weight of the specimen and W2 is the weight of the specimen after 30 cycles of the test.
Hardness test
Hardness is measured by scratching the mineral with series of substances of known variation in hardness using Mohs scale.
In general, Mohs invented a scale of hardness based on how one mineral scratched another. The Mohs’ scale is a not a linear scale. Instead it ranks gems on a relative scale based on their scratch hardness.
Hardness Number for different minerals based on Mohs scale are:
Mineral Scale Number
Talc 1
Gypsum 2
Calcite 3
Fluorite 4
Apatite 5
Feldspar 6
Quartz 7
Topaz 8
Corundum 9
Diamond 10
Types of rock
Sedimentary Rocks ⇒
- Rocks formed by accumulation, compaction, and consolidation of sediments are sedimentary rocks. It is also known as secondary rocks.
Examples:
- Breccia, Limestone, Sandstone, Shale
Metamorphic Rocks ⇒
- Rocks formed due to metamorphism (process responsible for all the changes that take place in an original rock under the influence of changes in the surrounding, conditions of temperature and pressure) are known as metamorphic rocks.
Examples:
- Quartzite, Marble, Slate, Phyllite, Schist, Gneiss
Igneous Rock ⇒
Rocks formed due to cooling or solidification of magma or lava is known as igneous rocks.
There are two types of igneous rocks:
Intrusive Igneous Rocks →
- These rocks are formed due to cooling/solidification of magma within the crust of a planet. It is also known as Plutonic Rock.
Examples:
- Dike, Sill, Granite, Laccolith, etc.
Extrusive Igneous Rocks →
- These rocks are formed due to cooling/solidification of magma at the crust’s surface. It cools faster than the intrusive one.
Examples:
- Basalts, Traps, Black Smokers, etc.
Quarrying is the process of removing the rock, sand, gravel or other minerals from the ground in order to use them to produce materials for construction or other uses.
Natural bed of stone is the plane along which stone can easily be split. It thus indicates the plane or bed on which the sedimentary stone was originally deposited.
Dressing of Stone is the working of quarried stone into the shape and size required for use. This can be necessary as stones obtained from quarrying generally do not have the exact required dimensions or finish.
Seasoning of stone means to expose the stone in the open air for a period of 6 to 12 months. It removes quarry sap and makes the stone-hard and compact.
